1. Field of the Invention
The present invention relates to improved inorganic media for dry barrel finishing. The dry barrel finishing herein means barrel finishing using no water that is conducted for removing flushes, rounding edges, leveling and burnishing of an article to be finished. The inorganic media of the invention can be used in various barrel finishing apparatuses such as rotary barrel, vibration barrel, flow barrel and centrifugal barrel.
2. Description of Related Art
As media used in the dry barrel finishing (particles having abrasive power), those having an arbitrary shape, such as a sphere, a triangular pyramid and a triangular prism, in a size of from several millimeters to several tens millimeters have been used. The media generally comprise an abrasive compound assuming the abrasive power and a binder (matrix) maintaining the abrasive compound to substantially constitute the media. The media are roughly classified into three classes, organic media, metallic media and inorganic media, depending on the main component of the binder.
The organic media are generally obtained by mixing and heating an inorganic abrasive grains and a binder such as a polyamide resin, followed by forming, as described, e.g., in Examined Published Japanese Patent Application No. 6-55446. While the barrel finishing using the organic media causes less roughening of a finished surface due to their soft nature, they have a small specific gravity and small abrasive power. The organic media are thus used for intermediate finishing such as leveling.
The metallic media are composed of metal balls themselves, as described, e.g., in Unexamined Published Japanese Patent Application No. 60-180765. Since the metallic media do not contain an abrasive compound, substantially no abrasive power is expected. They are used for fine finishing (mirror finishing) such as polishing utilizing their function of crushing and leveling micro-projections on the surface of an article to be finished.
The inorganic media are formed by sintering a mixed material of abrasive grains such as alumina and an inorganic binder such as bauxite, as described, e.g., in Examined Published Japanese Patent Application No. 44-23873. Since the inorganic media are inexpensive and have large abrasive power, they are used for rough finishing. The rough finishing herein is the opposite of the fine finishing and includes flush removal and edge rounding.
In the wet barrel finishing, a mass composed of works (articles to be finished), media and abrasive water is filled in a finishing barrel, and the mass is fluidized by rotation, revolution or vibration of the barrel or rotation of a rotating plate equipped at the bottom of the barrel to conduct finishing. As a result of flow of the mass, flush removal, edge rounding, leveling or polishing is conducted by friction between the works and the media. The wet barrel finishing has a characteristic feature in that a large number of articles having a complicated shape can be treated at once, and it has been employed in production processes of a wide range of products. However, the wet barrel finishing requires disposal ment of waste abrasive water, and there is a demand for making the waste water treatment easier.
In order to solve the above problem associated with the wet barrel finishing, various dry barrel finishing methods using no abrasive water have been proposed.
A dry barrel finishing is proposed in which a spindle oil or a fat and oil is used instead of abrasive water, as described, e.g., in Examined Published Japanese Patent Application No. 50-13994 and 57-57105. In this method, however, the oily component adhered on the articles to be finished must be removed when the following step is coating or plating. Thus, in this dry barrel finishing, waste water generates after washing the oily component, and as a result, a problem of waste water treatment arises.
Another dry barrel finishing is proposed in which no liquid material is added, as described, e.g., in Unexamined Published Japanese Patent Application No. 50-13994. However, the use of this finishing method is generally limited to final finishing such as polishing.
When rough finishing is conducted according to this dry barrel finishing using an inorganic media, the abrasive power (sharpness) of the inorganic media is soon decreased, and rough finishing cannot be stably conducted. The reason of the use of inorganic media is that the inorganic media has the largest abrasive power among the three types of media.